During fabrication of a semiconductor device, a wafer serves as a substrate for microelectronic devices built in and over the wafer and may undergo many microfabrication process steps such as doping or ion implantation, etching, deposition of various materials, and photolithographic patterning. Finally, the individual microcircuits are separated (dicing) and packaged.
Microelectromechanical systems (MEMS) is a technology of microscopic devices, particularly those with moving parts. MEMS became practical once they could be fabricated using modified semiconductor device fabrication technologies, normally used to make electronics. Thus, a MEMS may be built into a substrate as a component of an integrated circuit, that is diced into a semiconductor chip that is subsequently mounted in a package.
A protective material may be dispensed extensively all over the semiconductor chip and package at the end of the assembly process (i.e., filling of a cavity within the package). In some cases, particle protection is realized via a lid construction that is disposed over an opening of the package.
When a protective material is dispensed at the end of the assembly process, particles from a preassembly processes (i.e., prior to mounting the chip to the package) or a foregoing assembly process can reach the surface of a MEMS element or device. While miniaturization of MEMS elements evolves, smaller and smaller particles are playing a role, and are at the same time becoming more difficult to detect and screen. Furthermore, using a lid for particle protection does not provide absolute protection from humidity.